In general, dot matrix printers can be separated into two types of printers--line printers and serial printers. Both types of printers create images (characters or designs) by selectively printing a series of dots in an x-y matrix. A serial dot matrix printer includes a head that is moved back and forth across a sheet of paper, either continuously or by steps. The head includes a column of dot printing elements. As each column position of a character position is reach during printing, the required number of dot printing elements are actuated to form dots. A series of thusly created dot columns forms the desired character. Contrariwise, line printers include dot printing mechanisms for creating lines of dots substantially simultaneously as paper is stepped through the printer. A series of lines of dots creates an image, i.e., a row of characters or a design. The present invention is related to dot matrix line printers, as opposed to serial dot matrix printers.
In the past, various types of dot printing mechanisms for use in dot matrix line printers have been proposed and used. In one such printing mechanism a print comb, comprising a plurality of cantilevered print hammers formed of a resilient ferromagnetic material, is mounted on a carriage. The carriage shuttles the print comb back and forth in front of a plurality of electromagnets positioned so as to be able to selectively actuate the hammers. Hammer actuation is created by energizing the electromagnets to pull the free ends of the hammers away from the plane of the print comb and then releasing the thusly cocked hammers by de-energizing the energized electromagnets. The released hammers fly forward through the plane of the print comb and create a dot on the paper. Shuttling of the print comb results in each hammer "scanning" a predetermined number of dot positions of the overall print line. At each dot position, as required, the appropriate hammers are actuated to create dots in the manner heretofore described. After shuttling in one direction, the paper is indexed and the print comb is shuttled in the opposite direction, whereby the next line is scanned. A more detailed description of a printer that functions in this manner is set forth in U.S. Pat. No. 3,782,278, entitled, IMPACT LINE PRINTER assigned to Tally Corporation, Kent, Wash., the assignee of the present application.
As to be appreciated from the foregoing summary description the actuating electromagnets are mounted in a fixed position and only the print hammers are shuttled back and forth in a printer of the type described in U.S. Pat. No. 3,782,278. Alternative to a dot printing mechanism wherein only the print hammers are shuttled is one wherein the print hammer actuating mechanism as well as the print hammers are shuttled. A dot matrix line printer utilizing this approach is described in U.S. Pat. No. 3,941,051, entitled, PRINTER SYSTEM, by Gordon B. Barrus, et al. In addition to shuttling the hammer actuators as well as the hammers back and forth, U.S. Pat. No. 3,941,051 discloses the use of a permanent magnet to maintain the hammers cocked. The cocked hammers are released and their stored energy utilized to create a dot by the application of electrical energy to a coil wound around a pole piece to which the free end of the hammers are attracted. The coil creates a magnetic field that counteracts the permanent magnet field force such that the related cocked hammer is released. The present invention is directed to an improved and different type of dot printing mechanism for dot matrix line printers wherein the print hammer actuating mechanism as well as the print hammers are shuttled and wherein the print hammers are cocked by the magnetic field produced by a permanent magnet and released when a counteracting magnetic field is produced by an electromagnet.
Therefore, it is an object of this invention to provide a new and improved dot printing mechanism for dot matrix line printers.
It is another object of this invention to provide a new and improved dot printing mechanism for dot matrix line printers wherein the print hammer actuators as well as the print hammers are shuttled back and forth.
It is yet another object of this invention to provide a new and improved dot printing mechanism for dot matix line printers that utilizes permanent magnets to cock the print hammers, which are released upon the application of electrical energy to a release coils positioned so as to conteract the print hammer magnetic retraction force produced by the permanent magnets.